Musannaf Ibn Abi Shayba 13:3366

Abu Bakr narrated to us, he said: Muhammad ibn Yazid narrated to us, from Muhammad ibn Muslim, from Ibrahim ibn Maysara, from Tawus, who said: If I were to see a man split open the head of another man, and he called me to a tyrant (judge) to testify for him, I would not testify for him.